[media] soc_camera/pxa_camera: Constify struct dev_pm_ops

struct dev_pm_ops should be const.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>